1. Field of the Invention
The present invention relates to an electronic watermark generating apparatus, an electronic watermark verifying apparatus, a method of generating an electronic watermark, and a method of verifying an electronic watermark.
2. Description of the Related Art
In recent years, a technology called smart grid has been gaining attention. The smart grid is a technological framework to realize efficient power usage by constructing a new transmission network having a communication channel along with the transmission network and using this intelligent transmission network. The background idea of the smart grid is to realize efficient management of the amount of power use, swift handling of an incident when such an incident occurs, remote control of the amount of power use, distributed power generation using power generation facilities outside the control of a power company, or charging management of an electric vehicle. Particularly, effective utilization of in-house power generating stations using renewable energy by ordinary households or operators other than power companies and charging management of various electric vehicles typically including electric cars have been attracting considerable attention. Incidentally, renewable energy is energy generated without using fossil fuel.
Power generated by ordinary households or operators other than power companies is used by power generation operators. Remaining power after use by the power generation operators is currently purchased by power companies. However, purchasing power supplied from power generation facilities outside the control of a power company is a heavy burden to the power company. For example, amount of power supplied from photovoltaic power generation facilities depends on the weather. Moreover, amount of power supplied from in-house power generating stations of ordinary households depends on power use of ordinary households that largely changes day by day. Thus, it is difficult for power companies to receive stable power supply from power generation facilities outside the control of power companies. For the above reason, it may become difficult for power companies to purchase power in the future.
Thus, a home battery initiative that uses power generated by power generation facilities outside the control of power companies after temporarily storing the power in batteries has recently been gaining attention. For example, a method of using power generated by photovoltaic power generation facilities by storing such power in batteries and making up for shortages in the night or when the weather is bad is considered. Furthermore, a method of limiting amount of power received from a power company in accordance with the battery storage amount or using power stored in batteries in the daytime when power rates are higher by storing power, in batteries, supplied by a power company in the night when power rates are lower are considered. Also, batteries can store power as DC, which makes DC/AC conversion or AC/DC conversion during transmission unnecessary so that losses during conversion can be reduced.
Thus, various expectations regarding power management mingle with one another amid the smart grid initiative. To realize such power management, the smart grid initiative is premised on having a communication channel along with a transmission network. That is, exchanging information about power management by using this intelligent transmission network is assumed (see JP-A-2008-109849, for example). However, in a region where a communication infrastructure is already built, instead of using a transmission network as a communication channel, information about power management may be exchanged by using a network constructed by the deployed communication infrastructure.
With the above in mind, the patent document mentioned above proposes a technology of operating, from a remote place, an electronic appliance that is subject to power management, and makes an attempt to improve a user's convenience.